To solve the problem of matching the United Nations Secretary Generals with their citizenships at the time of appointment, we need to align each person's name with the correct country based on historical data:
A. Kurt Waldheim
1. Austria
B. Kofi Annan
4. Ghana
C. Antonio Guterres
3. Portugal
D. Ban Ki Moon
2. South Korea
Reviewing the options and matching each name with the proper country:
Kurt Waldheim was appointed from Austria, so A matches with 1.
Kofi Annan was from Ghana at the time of his appointment, so B matches with 4.
Antonio Guterres is from Portugal, so C matches with 3.
Ban Ki Moon was from South Korea, so D matches with 2.
The correct assignment based on this information is: A1, B4, C3, D2.